Captivated screw



July 12, 1966 H. c. CURTIS CAPTIVATED SCREW Filed Aug. 27, 1964 INVENTOR. Hzeeser aver/f BY w A rraavsv United States Patent 3,260,989 CAPTIVATED SCREW Herbert C. Curtis, Milwaukee, Wis., assignor to Curtis Development & Mfg. (30., Milwaukee, Wis. Filed Aug. 27, 1964, Ser. No. 392,445 1 Claim. (Cl. 339-272) This invention relates to improvements in captivating or keeping screws associated with a part into which the screw is threaded and which screw is to press on or be threaded into another part.

In the electrical terminal structure disclosed in U.S. Patent 3,135,572 issued to H. C. Curtis et al. on June 2, 1964, a tube 28 receives a pressure strip 29 adapted to bear on an electrical conductor under pressure of screws 30 threaded into holes in one side of the tube. The initial placing of such screws in the tube requires appreciable time; and may result in dropping screws during installation of the terminal block, which is of particular importance when the dropped screws can damage either parts or electrical circuits into or on which the screws fall. Accordingly purchasers of the above terminal and of like parts may specify that the screws be in place and even may specify the number of turns which the screws are to be given into the tube. However even such placing of screws does not assure that the screws will not be lost or dropped where they are difiicult to recover or may cause damage, either during installation of the terminal structure or servicing of associated parts.

Further, the pressure strip of the above terminal has heretofore been resilient and has been attached near its midpoint to a part of the tubular connector to retain the strip when it is not under pressure, while allowing either end or both ends of the strip to bend downwardly to press on a conductor. Such strip how-ever may take a permanent-set due to its limited length, which hinders changes in use, and assembly of the strip requires additional time in placing the strip within the tube.

Accordingly the present invention provides means which perform the dual function in the terminal block, of captivating a screw to the terminal tube and of serving as the pressure strip to prevent damage to the end of an electrical conductor to be held in the terminal tube. Further, a similar device may be used in captivating screws to other mechanical parts wherever a groove can serve in place of the space defined by the tube. And the captivating-pressure strip may be used to bear on another part or may be free from such other part as shown in modifications herein.

In the drawings:

FIG. 1 is a cross sectional view of a terminal block using a tube, with a screw and the present captivatingpressure strip for holding the end of an electrical conductor in good conductive contact with the tube.

FIG. 2 is a perspective showing the screw and captivating and pressure means of the present invention, both assembled with and disassembled from the terminal tube and from one another.

FIG. 3 is a cross section on the plane of line 33 of FIG. 1 to show the proportions between the neck of the screw and the opening of the captivating-pressure strip, receiving the screw neck.-

FIG. 4 is a blank of the captivating-pressure means to show the relationship between different areas thereof.

FIG. 5 is a cross section through two bars or the like showing a modification of the present invention when the captivating means is not acting between two parts to be joined.

FIG. 6 is a cross section of another modification of the present invention with the screw shown in retracted posi tion, in which a U-shaped captivating means is used, the leg previously forming the pressure tab now having a hole for passing the screw, and

FIG. 7 is a view similar to FIG. 6 showing another part in cross section with the screw drawing the second part against the first part.

Referring specifically to the drawings, reference numeral 10 designates a block of insulating material having spaced flanges 11 between which an electrical conductive terminal connector is to be placed. The insulating block used, is as shown in the above patent and no further description is believed necessary herein. The spaces between the flanges 11 are adapted to receive an electrically conductive terminal tube 12 which is preferably rectangular and has outside dimensions fitting a tube snugly into a space between a pair of flanges, the tubes extending sub stantially the width of the block body. The tube 12 has two holes 15 adjacent to the ends and through one side of the tube, and such holes are threaded to receive screws 16. Another hole 17 extends through two sides of the tube at about the tube midpoint to receive a pin 18 seating in the block 10 to hold the terminal tube in place relative to the block.

The screws 16 have an undercut 22 below the head to form a neck which is of less diameter than the threaded portion 23 of the screw. A substantially U-shaped captivating-pressure strip 24 has relatively wide and narrow legs which are spaced from each other for a distance approximately equal to the length of that portion of the screw between its neck and its free end. The narrow leg is slightly less wide than the interior of the tube to be received therein. It is interposed between the free end of the screw and the wall of the tube which is opposit th tube opening in which the screw is threaded.

The wider end of the U-shaped strip is engaged with the neck of the screw. Its thickness is substantially equal to the length of the screw neck portion. It has an opening in which the screw neck portion is rotatably positioned, being releasably engaged therein through a slot which bifurcates the wder leg of the U-shaped strip and which forms laterally yieldable prongs 25. The width of the slot is slightly less than the diameter of the neck portion of the screw. The side margins of the slot are generally parallel except at the rid of said wider legs where the margins flare divergently to facilitate engagement with the neck of the screw when the narrower leg is inserted in the tube and the wider leg is engaged with the neck portion of the screw. The screw neck 22 is made to fit snugly between the prongs but permits the screw to turn freely. 1

For example, the screw illustrated has a neck of .145 inch diameter while the prongs 25 are made with a circular area 27 of approximately the same diameter but with a parallel walled entry area 28 which is only .143 inch wide. Hence the prongs 25 must spring apart to allow seating of the captivating-pressure member 24 on the screw neck and must then reclose around the screw neck. For some thicknesses of material, the prongs 28 will spring sufiiciently without special structure. For other thicknesses of material, however, it has been found necessary to provide a slot 29 to increase the flexibility and resilience of the prongs. The thickness of the strip 24 generally determines the length of the screw neck (except in the modification of FIGS. 6 and 7) as it is desirable to seat the prongs 25 loosely on several neck surfaces so that leg 26 cannot bind in the tube 12. The

3 width of the tube 12 determines the width of the pressure tab 26. For example, in a tube width of .140 inch, a tab width of .136 inch is satisfactory. The length of the pressure tab 26 is sufiicient to distribute the pressure of the screw 16 over the end of the electric conductor 13 to be held thereby in the tube 12,

The parts are assembled by first threading the screw into the terminal tube. The narrow end of the strap is then inserted into the tube in contact with the clamping end of the screw and the prongs of the wider end are concurrently engaged with the neck of the screw under sufiicient pressure to spread the prongs to allow the neck port-ion of the screw to enter the hole, in which it rotates in use.

Thereafter the screw and strap will move axially as a unit to and from a position to transmit clamping pressure from the screw through the narrow leg to a conductor disposed within the tube in abutment with the tube wall which is opposite the opening. Any tendency of the strap to turn with the screw will be resisted due to the proximity of the intermediate portion of the strap with .the side walls of the tube, the intermediate portion being wider than the narrow leg and therefore laterally spanning the terminal end and being in sufficient proximity to engage the end surface of the tube in the event of substantial lateral dis-placement. Thus the strap is maintained substantially parallel to the exposed surface at the end of the tube.

The present construction can also be used for other purposes as is shown in FIG. in which one mechanical part is to have attached thereto another mechanical part 36, by use of a screw 37. Part 35 has a hole 38 which is unthreaded and which is of a size to pass the threaded screw portion without affecting screw movement. A groove 39 is cut in a surface of the part 35 parallel to the axis of the screw hole 38, to receive a tab 40 of a captivating member 41. Such member 40 is also made with prongs 42 to engage the screw neck 43, the proportions of the screw neck and the opening between the captivating member prongs being preferably as described above.

Referring to FIGS. 6 and 7, a captivating-pressure member is generally of the same shape as in FIGS. l-4, for aiding in joining two mechanical parts such as bars 51 and 52. Member 50 is U-shaped and formed with a leg 54 with prongs such as shown in FIGS. 3 and 4, while leg 55 is provided with a hole 56. The member 50 is of a size to seat snugly around the end of bar 51 and the circular portion of the prong opening and the hole 56 are aligned and concentric with hole 60 in bar 51. Holes 56 and 60 are larger in diameter than the threaded portion 61 of screw 62. The screw 62 is now provided with a neck 63 from the head of the screw and of a length no greater than the thickness of bar 51 and of leg 54, so that the head :of the screw may bear on the leg 54 when the screw thread 61 is substantially entirely engaged in the thread in the hole in bar 52 and draws the bars together. Thus the hole in bar 52 and screw portion 61 are the only threaded -arts required to draw the bar tightly against leg 55 and one side of bar 51 when the head of the screw 62 bears on the leg 54 and on the other side of bar 51.

Obviously it is immaterial in FIGS. 1-5 where the neck is formed on the screw so long as the length of the screw below the neck is greater than the distance the screw is to be run before the captivating member engages the top or the bottom of the tube space, or the ends of the groove in the part in FIG. 5. The screw neck dimension axially of the screw is greater than the thickness of the material of the prongs so that there is no tendency for the prongs to seat at an angle to the axis of the screw while the screw neck turns freely between the prongs. In FIGS. 6 and 7, the neck extends from below the screw head and is of a length substanitially equal to the thickness of one part and one leg of the captivating member. The diameter of the screw neck is slightly less than that of the circular area between the prongs so that the screw will turn freely about the screw neck and so that the captivating tab positions itself for free running in the cavity in parts 12 or 35.

The width and length of the slot 29 giving increased flexibility to the prongs, are such that the prongs may spring open to engage the screw neck and may reclose, and are dependent on the material used for the captivating means. The present captivating member makes a screw head unnecessary if the screw merely acts between its thread and the end as shown in FIG. 1, land is therefore useful even where headless screws are required.

The structure of FIG. 6 may be assembled by seating member 50 on bar 51 and then bending back leg 54 so that the threaded screw portion 61 may be placed in the hole 60 in bar 51 and may even extend through the hole 56 in the leg 55. The screw neck 63 is now positioned so that the prongs of leg 54 can be forced around the screw neck to bring it into the circular area between the prongs, and to seat the leg 54 on the bar 51 as shown in FIG. 6. However, the structure of FIG. 6 may also be assembled by first bending leg 55 toward alignment with the part of the captivating member between the two legs 54 and 55. The screw neck 63 is then placed between the progs of leg 54 and the screw threaded portion 61 then extends approximately parallel to the backward bent leg 55. The screw thread 61 is then drawn toward the leg 54 as far as possible and inserted in the bar hole 60. Leg 55 is then bent back against the side of the bar 51 whreby the screw is fully captivated.

I claim:

In a device for clamping an electrical conductor, the combination with a tubular electrical terminal having top, bottom, and side walls and an open end provided with an exposed surface, said terminal being provided in one wall with a threaded opening, of a conductor-clamping screw in said opening having a head and a neck portion of reduced cross section and threads engaged with said one wall, said screw having a clamping end within the tube, and means for holding the screw in captive connection with the terminal and for transmitting pressure of said end to hold a conductor within the terminal and comprising a strap of U-shaped form having spaced relatively wide and narrow legs and a substantially flat shouldered intermediate portion to which said legs are normal, the legs being spaced by a distance equal to the spacing between said neck and said clamping end of the screw, said wide leg being bifurcated at its extremity and being generally equal in thickness to the length of the screw neck portion and provided with an opening and with a slot opening thereto with generally parallel edges spaced at a distance slightly less than the diameter of the neck portion of the screw and outwardly divergent at the end of the wide leg of said strap and defining laterally yieldable prongs engaged with the screw neck portion between said one wall and the screw head, and the narrow leg being slightly less wide than the interior of the tube and extending into the open end of the tube in a position in which it underlies and is engaged by the clamping end of the screw, the strap being applicable longitudinally of the tube by concurrently inserting the narrow end into the tube in contact with the clamping end of the screw and engaging the prongs of the wider end with the neck of the screw, the screw and strap there-afiter moving axially as a unit to and from a position to transmit clamping pressure from the screw through said narrow leg to a conductor disposed within the tube in abutment with the tube wall opposite said opening, said strap intermediate portion being wider than said last mentioned leg and laterally spanning the terminal end and being in sufficient proximity to the said exposed surface at the sides of said terminal end to engage said surface in the event of substantial lateral displacement and thereby tobe maintained substantially parallel to said exposed surface.

(References on following page) 5 6 References Cited by the Examiner FOREIGN PATENTS UNITED STATES PATENTS 33,22? lljrance. 2,193,202 3/1940 Millermaster 339-472 1/1954 g ggh 2,590,450 3/1952 Parsons 151 41.75 5

2,882,513 4/1959 Olashaw 337-272 EDWARD C. ALLEN, Primary Examiner. 

